Dustproof fabric worn in a clean room

ABSTRACT

A dust-proof fabric is disclosed. The fabric comprises an inner knit fabric layer, an intermediate layer of a moisture absorbent polyurethane film and a high density woven polyester fabric outer layer. The outer layer contains a first set of spaced apart conductive yarns aligned with one another in the warp direction and a second set of spaced apart conductive yarns aligned in the weft direction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dustproof fabric and to a method ofmanufacturing the same. More particularly, the present invention relatesto a dustproof smock worn by technicians in the clean room and to amethod of manufacturing the fabric of the smock.

2. Description of the Related Art

Clean rooms are being used more often in a great number of differentareas including semiconductor fabrication facilities. The requirementsfor maintaining cleanliness in semiconductor fabrication clean rooms arestringent. Even the smocks worn by technicians in clean roomenvironments must be carefully designed and manufactured to prevent theclean room from being contaminated by dust or moisture emanating fromthe bodies of the technicians themselves (now referred to as"particles").

The first semiconductor devices to be manufactured were not nearly ashighly-integrated as the semiconductor devices which are manufacturedtoday. In the past, the clean rooms were maintained at a cleanlinessclass level of between 10 k and 100 k, and the smocks worn by thetechnicians in the clean rooms were made of nylon or polyester taffeta.

However, the semiconductor device fabrication process continues tobecome more and more affected by the environmental conditions existingin the place in which the process takes place. Such conditions includethe level of particulate contaminants, the electrostatic level of theair, etc. Accordingly, more attention has been paid to the material ofthe smocks worn by the technicians in the clean room. In this respect,polyester smocks have been adopted for use in the clean room.

Recently, highly integrated semiconductor devices having criticaldimensions on the order of sub-microns, such as the 64M DRAM, 256M DRAM,etc., have been developed. The clean rooms in which such devices aremade must be maintained at a cleanliness class of less than 10 k. Thisrequirement has brought about an even greater scrutiny of the fabricfrom which the clean room smock is made.

Even the ultra-fine filaments of the nylon taffeta or polyester taffetaof the conventional clean room smocks could not prevent anunsatisfactory amount of moisture or fine particulates from emanatingfrom workers' bodies into the clean room environment. The warp and weftof such fabric is just too great. Therefore, such fabric was treatedwith a moisture-permeable and water-proof, water-repellent coating orlaminate of polyurethane resin or fluoric resin. Fabric treated in thisway is shown in FIG. 1, and is manufactured by The Dupont Company ofDelaware under the trademark GORETEX.

Referring now to FIG. 1, a polyester fabric 3 woven from alignedconductive yarns 2 is coated with a polyurethane and/or fluoric resinfilm 1. As shown in FIG. 2, particles emanating from one's body cannotpass through the coated resin film 1, but moisture from the body canpass through fine pores of the fabric. Accordingly, the fabric ismoisture-permeable. On the other hand, water molecules having arelatively large size cannot permeate the pores 14 of the coating layer15 and may become stuck. Thus, the moisture permeability decreases, andthe comfort level of wearing the fabric is somewhat compromised. Thecomfort level is even lower when the resin layer 1, 15 is located at theside of the fabric which contacts the skin.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome one or more of theproblems, limitations and disadvantages of the related art.

Accordingly, a first specific object of the present invention is toprovide a dustproof fabric which is impermeable to particles of 0.1microns or larger.

Another specific object of the present invention is to provide adustproof fabric having a relatively high degree of water-permeabilityand which is very comfortable when worn.

To achieve these objects, the dustproof fabric of the present inventioncomprises three integrated layers. The inner layer is of a knittedfabric. The intermediate layer is formed of a non-micro porouspolyurethane resin exhibiting a high degree of moisture absorbency. Theouter layer is formed of a high density polyester woven fabric havingwarps and wefts of respective sets of spaced apart conductive yarns.

The knit fabric of the inner layer is preferably a warp-knitted fabricof nylon tricot having good strength and resilience.

The intermediate layer and the inner layer are preferably attached bydots of hot-melt adhesive so that the fabric retains a sufficient degreeof flexibility. On the other hand, the intermediate layer and the outerlayer can be attached by dots or by a thin coating of adhesive.

The high density polyester woven fabric of the outer layer may alsocomprise ultra-fine yarns having a filament denier of 0.1 or less. Suchyarns can be produced by the so-called sea and island type or separationtype of conjugate spinning.

As far as the pattern of the high-density polyester woven fabric of theouter layer is concerned, a 2/1 Twill and in particular, a Herringbonetwill is preferable.

The objects of the invention are also achieved by a method ofmanufacturing a dustproof fabric comprising the steps of: (a)manufacturing a woven fabric, having a warp density of 140 to 170 yarnsper inch and a weft density of 90 to 130 yarns per inch, from polyesteryarns having a yarn denier in a range of 50 to 100 and conductive yarnshaving a yarn denier in a range of 15 to 30, with the conductive yarnsaligned with one another and spaced apart in both the warp and weft; (b)coating release paper with non-micro porous polyurethane resinexhibiting a high degree of moisture absorbency, attaching the wovenfabric to the polyurethane, and drying the same (c) aging the integratedlayers sufficiently to facilitate a cross-linking reaction in thepolyurethane resin layer, and detaching the release paper therefrom; and(d) attaching nylon knit fabric to the polyurethane layer, and aging thesame.

In addition, the high-density woven fabric of the outer layer ispreferably subjected to an anti-static treatment of a per se known type.

A clean room smock of the fabric described above is made dustproof bythe polyurethane film provided on the high-density woven fabric.

In fact, ultra-fine particles from the human body, which range in sizefrom 0.001 to 0.1 μm, are prevented from passing through the smock bythe intermediate layer of polyurethane film according to the presentinvention.

Moreover, because of the high degree of moisture permeability exhibitedby the polyurethane layer, a smock made from the dustproof fabric isvery comfortable to wear.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of preferred embodiments thereof made with reference to theaccompanying drawings, of which:

FIG. 1 is a schematic diagram of a conventional dustproof fabric for usein a clean room in which a semiconductor device fabrication processtakes place;

FIG. 2 is a schematic diagram of a cross-sectional view of the coatingof the conventional dustproof fabric and showing moisture moleculespassing through the coating;

FIG. 3 is a schematic diagram of the dustproof fabric for use in a cleanroom according to the present invention;

FIG. 4 is a block diagram of the sequences of steps of the method ofmanufacturing the dustproof fabric according to the present invention;

FIG. 5 is a schematic diagram of a cross-sectional view of the coatingof the dustproof fabric according to the present invention and showingmoisture molecules passing through the coating of the fabric; and

FIG. 6 is a perspective view of a smock.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 3, the dustproof fabric comprises an inner layer103 of a knit fabric, an intermediate layer 102 and an outer layer 101.The outer layer 101 is a high density polyester woven fabric. Besidespolyester filaments and ultra-fine yarns having a filament denier of atmost 0.1, the fabric of the outer layer 101 is formed of conductiveyarns 104 aligned with one another in the directions of the warp andweft and slightly spaced apart from each other in each of suchdirections. The weaving density T of the outer layer 101 is in a rangeof 230 to 300 (wherein T is the sum of the numbers of filaments per inchin each direction of the warp and weft, and is an industry norm fordesignating density). The high density woven fabric is extremelydustproof because it has a low degree of porosity.

Various types of conductive yarn 104 can be employed in the outer layerof the high density woven fabric of the present invention. Such yarnsinclude those having a core filament whose surface is covered withcarbon, and those whose filaments are impregnated with carbon by meansof conjugate spinning, etc. The spacing of the conductive yarns 104 inthe warp and weft of the outer layer is preferably in a range of 0.3 to1 cm, in consideration of weaving efficiency and of achievingsatisfactory conductivity.

The denier of the polyester filaments of the woven fabric of the outerlayer 101 is within a range of 50 to 100, whereas the denier of theconductive yarns 104 of the fabric is within the range of 15 to 30,which ranges are also preferable in consideration of the weavingefficiency and conductivity.

The polyester woven fabric has a 2/1 Twill structure, and preferably isof a Herringbone twill, which is a highly resilient and highly densestructure.

The intermediate layer 102 of the dustproof fabric is situated under theouter layer 101. The intermediate layer 102 comprises a non-micro porouspolyurethane resin film exhibiting a high degree of moisture absorbency.The polyurethane resin is preferably one selected from the ester groupor the ether group. An adhesive layer is interposed between the outerlayer 101 and the intermediate layer 102. The adhesive layer should beas thin as possible so as not to unduly decrease the water-permeabilityof the structure. The adhesive can alternatively be in the form of dotsprovided by a dot-bonding method known per se.

As a result, moisture or sweat emanating from a human body and passingthrough the knit fabric of the inner layer 103 is absorbed by thehigh-density polyurethane resin film of the intermediate layer 102.There, the moisture or sweat is allowed to evaporate into molecules.These molecules are so small (0.001 μm or smaller) that they will notfunction to contaminate the semiconductor device fabrication processonce they pass through the polyurethane resin film and are dischargedfrom the outer layer 101 into atmosphere.

The knit fabric of the inner layer 103 and the intermediate layer 102are preferably attached by adhesive applied by dot-bonding. A hot-meltadhesive can be used for this purpose.

Referring now to FIG. 4, the dustproof fabric is manufactured by firstmanufacturing the high-density polyester woven fabric of the outerlayer, and secondly by manufacturing the high moisture-absorbencypolyurethane resin film of the intermediate layer using a transfercoating technique in which the resin is coated on a release paper. Then,the outer layer and the intermediate layer are adhered to one another.The method is completed by attaching the knit fabric of the inner layerto the intermediate layer. As shown by the dotted lines, a smock can bemade from such fabric by the conventional techniques of manufacturingclothing from fabric. Such techniques may include first providing apattern of the smock (or certain segments thereof) on the dustprooffabric/pieces of fabric, cutting the dustproof fabric/pieces of fabricalong the pattern, and stitching or otherwise securing the cut pieces offabric together to form the smock. FIG. 6 shows such a smock but thepresent invention is in no way intended to be limited to the specificshape/size/design of the smock depicted in the figure.

Describing the method in more detail, the high-density polyester wovenfabric of the outer layer is first woven, and then scoured, dyed, and isheat-set, i.e. dried (first step in the overall manufacturing process).

Next, a sheet of release paper is coated with a layer (skin) ofpolyurethane resin having a high degree of moisture absorbency toproduce the film of the intermediate layer. This layer is attached tothe high-density polyester woven fabric. Heat is then applied to causethe resin to set, whereby the second overall step in the manufacturingprocess is completed.

Next, the adhered outer layer and intermediate layer are aged.Afterwards, the release paper is detached from the polyurethane resin(third overall step).

Finally, the knit fabric is bonded to the intermediate layer, and theintegrated layers are aged (fourth step).

The weaving which is part of the first step is carried out by aconventional water jet loom. Such a loom is capable of producing aTwill, especially a 2/1 Twill such as a Herringbone Twill, previouslyreferred to as the most preferable form of the outer layer 101.

Because the polyester yarn forming the warp and weft of the polyesterwoven fabric of the outer layer, and the conductive yarn of the samelayer have different filament deniers, the strength and elongation ofthe polyester and conductive yarns are different. Accordingly, thetension applied to the warp and weft during weaving must be carefullycontrolled. In the fabric of the present invention, the warp density isin a range of 140 to 170 filaments per inch, and the weft density is ina range of 90 to 130 filaments per inch. Accordingly, the fabric has ahigh density in a range of 230 to 300 T. In addition, the denier of thepolyester yarns ranges from 50 to 100, and the denier of the conductiveyarns ranges from 15 to 30. Within these ranges, the fabric can be woveneasily, i.e. with high efficiency, and yet the resultant fabric iscomfortable to wear. The scouring, dying, and heat-setting can beeffected by conventional techniques used for processing polyester.

In order to enhance the resiliency of the fabric of the outer layer 103and its adhesion to the resin of the intermediate layer 102, thepolyester yarn is of a draw-twisted type. Furthermore, the fabric of theouter layer 103 can be subjected to an anti-static treatment after ithas been dyed to minimize its ability to generate static electricity.

As previously mentioned, the polyurethane resin of the intermediatelayer 102 is non-micro porous and exhibits a high degree of moistureabsorbency. In particular, those polyurethane resins in the hydrophilicester or ether group are preferable. It should also be noted thatconventional transfer coating machines are suitable for carrying out thesecond step of the method of the present invention, i.e. the formationof the film of polyurethane resin.

Regarding the third step, the integrated layers are preferably allowedto age at a temperature of 50 to 80° C. for over 15 hours. Suchconditions are sufficient to facilitate a cross-linking reaction in thepolyurethane resin film.

Regarding the fourth step, the integrated layers are also preferablyaged at a temperature of 50 to 80° C. for over 15 hours. The knit fabricof the inner layer 103 is preferably dot-bonded to the intermediatelayer 102 in order to ensure that the final product is sufficientlyflexible for use as clothing.

FIG. 5 is a model of the present invention showing that molecules ofmoisture will pass through the intermediate layer of the dustprooffabric of the present invention. Unlike the prior art, in which waterparticles are discharged through fine pores, particles of moisture 12are absorbed by the coating 13 (representing the intermediate layer102), diffuse toward the outside, and are discharged as molecules 11.That is, the present invention actually reduces the size of thepotential contaminants before they are allowed to pass through thefabric. Accordingly, a blockage of the pores can also be prevented.

Now, a specific embodiment of the present invention will be described indetail. It should be understood that this embodiment is provided only asan example of the present invention, and is not meant to limit the same.

EXAMPLE

The high-density woven fabric of the outer layer was manufactured by awater jet loom, and the space between the conductive yarns in both thewarp and the weft was 0.6 cm. The polyester filaments of both the warpand weft were of 70 denier, and the conductive yarns were of 20 denier.The weaving density was 165×115. The woven fabric was a 2/1 Twill.

The raw fabric was scoured in a consecutive scouring machine at atemperature of 90° C. at 60 mpm, dyed white using a circular dyingmachine, and heat-set in a tenter at a temperature of 140° C. at 60m/min.

A flat sheet of release paper was coated with a non-micro porouspolyurethane resin of the ester group at a temperature of 110 to 120° C.at 20 m/min. by using a consecutive coating machine. The result was inturn coated with an adhesive. Then, the high-density woven fabric andthe polyurethane resin coated with adhesive were compressed betweenrollers to adhere them together. The resulting structure was aged at atemperature of 60° C. for 24 hours to facilitate a cross-linkingreaction in the urethane resin.

The release paper was then removed. A nylon tricot Smith knitted fabricwas dot-bonded to the surface from which the release paper had beenremoved. The resulting structure was aged at a temperature of 60 to 70°C. for 24 hours, thereby completing the manufacture of the dustprooffabric.

The following table offers a comparison of the characteristics of thedustproof fabric of the present invention and the fabric of the priorart.

                  TABLE                                                           ______________________________________                                        Fabric Comparison                                                                        moisture                     air                                   particle   permea-  resis- film         permea-                               shield     bility   tance  strength                                                                            resilience                                                                           bility                                ______________________________________                                        dustproof                                                                            over    10000    Δ                                                                            ⊚                                                                    ⊚                                                                     0.11                                fabric of                                                                            99.9%                                                                  the em-                                                                              for                                                                    bodiment                                                                             0.1 μm                                                                     particle                                                               con-   over     8000    Δ                                                                            Δ                                                                             Δ                                                                              less than                           ventional                                                                            99% for                            0.05                                dustproof                                                                            0.3 μm                                                              fabric particle                                                               ______________________________________                                    

In the above table, the moisture permeability was detected by apotassium acetate method (KSK 0594 standard), and the air permeabilitywas detected by the Frazier method (KSK 0570). The symbol "Δ" representsan average performance value, and the symbol "○" represents anabove-average performance value.

A clean room smock made of the dustproof fabric of the present inventioncan be used in a clean room in which highly integrated semiconductordevices are produced. Such a smock will not allow such an environment,which must be maintained at a cleanliness class of less than 10 forparticles of 0.1 to 0.001 μm, to be contaminated.

The clean room smock according to the present invention is verycomfortable because moisture from the body passes easily through thesmock. The clean room smock is also made dustproof by the polyurethanefilm provided on the high-density woven fabric, and due to theanti-static treatment of the woven fabric and the corona dischargefacilitated by the aligned conductive yarn.

In fact, ultra-fine particles from the human body, which range in sizefrom 0.001 to 0.1 μm, are prevented from passing through the smock bythe intermediate layer of polyurethane film according to the presentinvention.

Although the present invention has been described in detail, variouschanges, substitutions and alterations thereto will become apparent tothose of ordinary skill in the art. All such changes, substitutions andalterations are thus seen to be within the true spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A dustproof fabric comprising:an inner layercomprising a knit fabric; an intermediate layer attached to said innerlayer and comprising a non-micro porous and moisture absorbentpolyurethane resin film; and an outer layer attached to saidintermediate layer opposite said inner layer, said outer layercomprising a high density woven fabric of polyester yarns, a first setof spaced apart conductive yarns aligned with one another in thedirection of the warp of the woven fabric, and a second set of spacedapart conductive yarns aligned with one another in the direction of theweft of the woven fabric.
 2. The dustproof fabric of claim 1, whereinsaid knit fabric of the inner layer is a warp-knitted fabric of nylontricot.
 3. The dustproof fabric of claim 1, wherein said intermediatelayer and the inner layer are attached by dots of adhesive.
 4. Thedustproof fabric of claim 1, wherein said intermediate layer and saidouter layer are attached by dots of adhesive.
 5. The dustproof fabric ofclaim 1, wherein said woven fabric comprises yarns having a filamentdenier of at most 0.1.
 6. The dustproof fabric of claim 1, wherein saidpolyurethane resin is selected from a group consisting of ether andester based resins.
 7. The dustproof fabric of claim 1, wherein saidpolyester woven fabric has a Twill structure.
 8. The dustproof fabric ofclaim 1, wherein the fabric has a moisture permeability of 10,000 asmeasured by a standard potassium acetate method.
 9. The dustproof fabricof claim 1, wherein the fabric has an air permeability of 0.11 asmeasured by a standard Frazier method.
 10. The dustproof fabric of claim8, wherein the fabric has an air permeability of 0.11 as measured by astandard Frazier method.
 11. The dustproof fabric of claim 1, whereinsaid woven fabric has a density in a range of 230 to 300 T.
 12. Thedustproof fabric of claim 8, wherein said woven fabric has a density ina range of 230 to 300 T.
 13. The dustproof fabric of claim 9, whereinsaid woven fabric has a density in a range of 230 to 300 T.
 14. Thedustproof fabric of claim 10, wherein said woven fabric has a density ina range of 230 to 300 T.
 15. The dustproof fabric of claim 1, whereinsaid conductive yarns are spaced from one another by 0.3 to 1 cm. 16.The dustproof fabric of claim 11, wherein said conductive yarns arespaced from one another by 0.3 to 1 cm.
 17. The dustproof fabric ofclaim 1, wherein said polyester yarns are draw-twisted.